The invention relates to a starting device for a discharge lamp, and in particular to a starting device for a high-pressure discharge lamp adapted to be located remotely from the ballast.
High-Intensity Discharge (HID) lamps produce light by driving current through a gas filled arc-tube. A light emitting discharge arc is produced between two electrodes exposed within the arc-tube. A starting device is required to initiate the arc between the two electrodes. Typically, the starting device must produce a pulse of several kilovolts across the two electrodes in order to initiate the arc and start the lamp.
Many conventional HID lamps require a ballast and starting circuit to generate a starting pulse and to supply the operating lamp with the necessary operating current. Conventional starting circuits charge a capacitor to a certain value until an automatic switch closes allowing the capacitor to discharge through the primary winding of a transformer. The primary winding is inductively coupled to a secondary winding, and the combination of the rapidly discharging capacitor through the primary winding, along with the winding ratio of the secondary winding to the primary winding, generates a pulse of sufficient voltage and duration across the electrodes of the HID lamp to initiate operation. Unfortunately, conventional ballasts and starting circuits have to be located relatively close to the HID lamp because parasitic impedances in the conductors connecting the HID lamp to the starting circuit tend to attenuate the starting pulse. Because of this effect of parasitic impedances, many ballast manufacturers place a maximum xe2x80x9clamp-to-ballastxe2x80x9d distance on every ballast-starter combination that is offered. These distances typically range from 2 to 75 feet, depending on the ballast and the ignitor circuit being used.
It would be advantageous to provide a starting circuit which is capable of starting and operating an HID lamp such that the lamp could be located at an unrestricted distance from the ballast.
The above-described disadvantages are overcome and other advantages are realized by providing a starting circuit in accordance with the present invention. According to the first embodiment of the invention, an ignitor circuit for a discharge lamp is provided which comprises a voltage input terminal, an ignitor output terminal, and a first capacitor having first and second capacitor terminals. The first capacitor terminal is connected to the voltage input terminal. The ignitor circuit further has a transformer having a primary winding inductively coupled to a secondary winding. An automatic switch is connected in series with the primary winding. The switch and primary winding are connected across the first capacitor, and the secondary winding is connected between the starting circuit voltage input terminal and the output or xe2x80x9clampxe2x80x9d terminal. A resistor is connected between the second capacitor terminal and the common terminal, and the second capacitor is connected across the resistor. The second capacitor is selected to have a value such that it represents a low impedance path for the high-frequency pulse generated by the transformer. Therefore, the pulse is de-coupled from the input lines and is presented across the electrodes of the discharge lamp.
In another embodiment of the present invention, an ignitor circuit for a discharge lamp is provided that comprises input terminals, an ignitor output terminal and a first capacitor having first and second capacitor terminals. The first capacitor terminal is connected to one of the input terminals. The ignitor circuit also has a transformer having a primary winding inductively coupled to a secondary winding. Furthermore, an automatic switch is connected in series with the primary winding, such that the switch and primary winding are connected across the first capacitor. The secondary winding is connected to the voltage input terminal and the ignitor output terminal. A resistor is connected between the second capacitor terminal and a common terminal, and a second capacitor is connected between the first input terminal and the second input terminal. In this embodiment the second capacitor presents a low impedance path for the high-voltage pulse generated by the transformer such that the pulse is applied across the terminals of the HID lamp.
In the third embodiment of the invention, an ignitor circuit for a discharge lamp is provided that comprises a voltage input terminal, an ignitor output terminal, and a transformer having a primary winding inductively coupled to a secondary winding. A resonant circuit is connected between the voltage input terminal and a common terminal, wherein the resonance circuit comprises the primary winding connected in series with an automatic switch and a first capacitor. The first capacitor is connected to the voltage input terminal. A second capacitor is connected in series to the secondary winding, such that the second capacitor and secondary winding are connected across the ignitor terminal and the common terminal. Finally, and inductor device is connected between the voltage input terminal and the ignitor terminal. In this manner, the high-frequency pulse generated in the secondary winding of the transformer is present across the terminals of the discharge lamp through the low impedance path of the secondary capacitor. Furthermore, the pulse is de-coupled from the input terminals by the inductor.